1. Field of the Invention
This invention relates to fluorine-containing polymers having excellent oxygen permeability, water swellability and contamination resistance and oxygen-permeable articles formed from the polymers. More specifically, this invention relates to oxygen-permeable articles which when used for medical or other purposes, for example as soft contact lenses, exhibit excellent properties such as bio-compatibility and can be worn for an extended period of time.
2. Description of the Prior Art
The cornea of the eye is an avascular tissue. Oxygen required for its aerobic metabolism is supplied by diffusion from the eyelid conjunction or aqueous humor during sleeping, but taken from the atmosphere during awaking. Accordingly, wearing of a contact lens, whether a soft or hard one, is liable to be an obstacle to oxygen supply. Wearing of the contact lens for an extended period of time often results in bloodshot eyes, edema, and other corneal disorders. Hence, a material for contact lenses is required to have excellent oxygen permeability in addition to excellent optical, chemical, physical and mechanical properties. Furthermore, contact lenses are required to have resistance to contamination by proteins, lipids and mucin which are the components of tear and to bacteria and eumycetes as well, excellent hydrophilicity, excellent water swellability, excellent wearing comfort and excellent bio-compatibility.
Polymethyl methacrylate (PMMA) and polymers of other various methacrylate ester monomers have been widely used as materials for contact lenses. Most of them have low oxygen permeability and cannot withstand wearing for an extended period of time.
To improve the oxygen permeability of conventional methacrylate ester polymers, there have been proposed, for example, a silicone methacrylate polymer having a siloxane linkage introduced into methacrylate ester molecules (Japanese Patent Publication No. 33502/1977), and an oxygen-permeable polymer composed mainly of cellulose acetate butyrate and a fluorine-containing methacrylate polymer (Japanese Laid-Open Patent Publications Nos. 51705/1982 and 111308/1986) as materials for contact lenses. These polymers have improved oxygen permeability over conventional methacrylate ester polymers such as PMMA, but their oxygen permeability is still not sufficient. Hence, polymers having still improved oxygen permeability have been desired. These conventional improved polymers, moreover, do not have satisfactory contamination resistance, hydrophilicity, water swellability and wearing feel.